#include <iostream>
#include <cstring>

using namespace std;

const int N = 510;

int n, m;

int g[N][N];
int dist[N];
bool st[N];

int dijsktra()
{
    memset(dist, 0x3f, sizeof dist);

    dist[1] = 0;

    for (int i = 0; i < n; ++i)
    {
        int t = -1;
        for (int j = 1; j <= n; ++j)
        {
            if (!st[j] && (t == -1 || dist[t] > dist[j]))
            {
                t = j;
            }
        }

        st[t] = true;

        for (int j = 1; j <= n; ++j)
        {
            dist[j] = min(dist[j], dist[t] + g[t][j]);
        }
    }

    if (dist[n] == 0x3f3f3f3f) return -1;
    return dist[n];
}

int main()
{
    memset(g, 0x3f, sizeof g);

    cin >> n >> m;
    for (int i = 0; i < m; ++i)
    {
        int a, b, c; cin >> a >> b >> c;
        g[a][b] = min(g[a][b], c);
    }

    int t = dijsktra();

    cout << t << endl;
    return 0;
}